Cellulosic materials, such as wood, paper, rayon and cotton, are used extensively in industry, public places and in the home as materials of construction or for decorative applications. All of these materials are highly flammable and require some form of treatment to impart fire retardant or flame resistant properties.
The conventional method for treating wood to impart fire retardant properties is pressure impregnation with fire retardant chemicals. The resulting wood is then kiln dried or air dried to a moisture content of 20% or less. Recently, it has been discovered that wood treated with currently available fire retardant formulations undergoes loss of structural strength. It is believed that this loss is the result of thermal degradation of the wood due to high temperature and humidity conditions. Many fire retardant formulations contain inorganic and organic phosphates. Typical inorganic phosphates consist of monoammonium phosphate, diammonium phosphate, ammonium polyphosphate or some combination thereof. These phosphates can cause the treated wood to thermally degrade under high temperature and humidity conditions. It is believed that ammonium phosphates, which are one type of ingredient commonly used in fire retardant formulations used to treat cellulosic materials, such as wood, may be responsible for the thermal degradation problem with this fire retardant treated wood. In this connection, it is believed that these ammonium phosphates when exposed to high temperature and humidity conditions for prolonged periods of time, as encountered in some roofing systems, may undergo hydrolysis to phosphoric acid. This phosphoric acid in turn reacts with the wood components causing the wood to char and become brittle, which ultimately results in the reduction of the strength properties of the wood. Similar effects have also been noted with some organic phosphates.
One such fire retardant formulation is that disclosed in U.S. Pat. No. 4,301,217. The formulation comprises an aqueous preparation which contains at least one water soluble ammonium salt of an inorganic acid such as ammonium sulfate or ammonium phosphate, at least one water soluble cationic reaction product of dicyandiamide or formaldehyde, and optionally an ammonium salt and an alkylenepolyamine. The wood is impregnated with the preparation using a single bath process or, alternatively, a two bath process and subsequently dried. It is believed that wood treated with this formulation may undergo thermal degradation due to hydrolysis of the ammonium sulfate or ammonium phosphate under high temperature and humidity conditions.
U.S. Pat. No. 2,482,756 discloses another formulation used for flame proofing fiberous materials which comprises mixing orthophosphoric acid and urea and heating the mixture to a temperature of from about 260.degree. F. to about 400.degree. F., preferably to about 365.degree. F. Thereafter, water, ammonia and an aldehyde are added to the solution. The fiberous material is then impregnated with the solution, dried and cured. The material impregnated with this formula exhibits durable flame proof properties. However, during the heating process, complex reactions take place between the phosphoric acid and urea and between the acid and the products formed by the alteration of the urea at the high temperatures such that carbon dioxide, ammonia and water are liberated. Thus, the urea is decomposed during heating, and consequently, any phosphoric acid resulting from the decomposition of the urea -phosphate complex will be neutralized by ammonia. This will result in the formation of ammonium phosphates. These ammonium phosphates will ultimately lead to the thermal degradation of the treated cellulose product. Furthermore, the formulation disclosed in U.S. Pat. No. 2,482,756 utilizes salts of strong acids with volatile bases, such as ammonium phosphate. As previously noted the presence of ammonium phosphate will result in thermal degradation of the cellulosic material when exposed to high temperature and high humidity conditions for an extended period of time.
Therefore, it would be desirable to provide a new and improved fire retardant composition for treating cellulose materials whereby the resulting treated wood exhibits good fire retardant properties and thermal stability when exposed to high temperature and humidity conditions.